Gas turbine engines are known to include a compressor for compressing air, a combustor for producing a hot gas by burning fuel in the presence of the compressed air produced by the compressor, and a turbine for expanding the hot gas to extract shaft power. The design of a gas turbine combustor is complicated by the necessity for the gas turbine engine to operate reliably with a low level of emissions, such as oxides of nitrogen (NOx), at a variety of power levels. In addition, it is important to ensure the stability of the flame to avoid unexpected flameout and damaging levels of acoustic vibration. A relatively rich fuel/air mixture will improve the stability of the combustion process but will have an adverse affect on the level of emissions. A careful balance must be achieved among these various constraints in order to provide a reliable machine capable of satisfying very strict modern emissions regulations over a wide range of loading conditions. A pilot flame is commonly used to stabilize the flame. However, the pilot is a diffusion flame that produces a significant amount of NOx.
Staging is the delivery of fuel to the combustion chamber through at least two separately controllable fuel supply systems or stages. Staging is known as a method to control combustion in a gas turbine combustor. A staged gas turbine combustor pilot is described in U.S. Pat. No. 6,877,307 as having a premix stage wherein air and fuel are premixed prior to being combusted in a pilot combustion region to achieve reduced pollutant emission.
Traditionally, gas turbine engine settings for a land-based powder generation turbine are manually “tuned” by a combustion engineer during the start-up of the power plant in order to satisfy appropriate emissions criteria without exceeding dynamic load limitations. As emission limits become increasingly stringent, low NOx combustors must be operated increasingly close to their physical limits and operational margins become smaller. A power plant turbine may be required to operate for days, weeks or even months. During such extended intervals, many variables affecting the combustion conditions may change. For example, the temperature and humidity of the ambient combustion air may change, the fuel characteristics may change, and the combustion system components are subject to wear and drift over time.